Nomogram for Individualized Prediction and Prognostic Factors for Survival in Patients with Primary Spinal Chordoma: A Population-Based Longitudinal Cohort Study

Background: Chordoma is a type of rare bone tumor and is a relatively slow-growing, low-grade malignancy that is locally invasive and aggressive. The nomogram is widely used in the field of cancer because it can provide a clear picture for clinicians to predict the survival rate, which can lead more accurate decisions in clinical treatment.

Methods: Overall, 875 patients with a primary spinal chordoma were identified and collected from the Surveillance, Epidemiology, and End Results registry databases (1973-2015). The nomogram was established based on 425 patients with complete data. The predictive accuracy and discriminative ability of the nomogram were determined by the concordance index (C-index) and calibration curve.

Results: The statistical nomogram was built on 10 independent prognostic factors: age, sex, race, disease stage, surgery, year of diagnosis, marital status, primary site, radiation, and tumor size, with C-indices of 0.76. The calibration curve to determine the probability of survival showed good agreement between the predictions by the nomogram and actual observation. Tumor diameter >10 cm (hazard ratio [HR] 2.95, 95% confidence interval [CI] 1.77-4.90, P < 0.001), regional invasive (HR 1.71, 95% CI 1.16-2.53, P < 0.01), and distant metastasis (HR 3.44, 95% CI 1.98-5.96, P< 0.001) were independent risk factors for poor survival. Undergoing subtotal resection or gross total resection (HR 0.37, 95% CI 0.25-0.56, P < 0.001; HR 0.26, 95% CI 0.17-0.41, respectively) and a primary site located in the sacrum/pelvis (HR 0.51, 95% CI 0.34-0.78, P < 0.01) were prognostic factors for better survival.

Conclusions: The nomogram provided more accurate prognostic predictions for patients with spinal chordoma. Moreover, our study suggests that tumor diameter >5 cm, distant metastasis, and not performing resection are major risk factors that can dramatically decrease the survival time of patients with spinal chordoma.